With the advent of the information age, it has become quite common for people to use electronic mail for message exchange; even in a case the message is very secret. In the meantime current electronic mailing systems are far from being safe because one engaged in a computer networking operation can easily eavesdrop on the communication by intercepting the messages. The only method to make an electronic mailing message secure is to use a cryptography method, i.e., the sender encrypts the sending message and the receiver decrypts the received message.
However, introducing an encryption-and-decryption method to an electronic mailing system creates the two important difficulties. Firstly, in the case where a symmetric key is used, it is necessary for the message sender and the message receiver to negotiate about the key they use before they start mailing. Such negotiation must be done in a very secret manner. This process, however, takes a significantly long time and needs considerable effort. Especially, when the sender and the receiver are not acquainted beforehand, the confidential negotiation is almost impossible.
Secondly, in the case where an asymmetric key is used, a message sender primarily needs to consult an authentication bureau to obtain the legitimate public key of the message receiver. This procedure also requires not only some time and effort, but also incurs some cost on the message sender's side, even if such a bureau is operated publicly.
Therefore there is a need for an electronic mailing system wherein a message sender can send a message anonymously and covertly, and in a symmetric key system a message sender and a message receiver need not negotiate about a key they use before they start mailing thereby negating the need for significant lengths of time and considerable effort, and in an asymmetric key system a message sender need not consult an authentication bureau to obtain the legitimate public key of the message receiver.